Pharaoh
Find the cat named "Pharaoh," who will be roaming about somewhere in the Slifer Red Dorms or the Ra Yellow Dorms. Pet its head, throat or back -- if it likes this it will follow you around. If not, give it a sandwich for the same outcome. Every time you talk to a character with the cat by your side, the conversation will go very well, making "Pharaoh" perfect for building relationships. Unfortunately, the cat will leave you after one day.
Free DP Email
You will receive an email on your PDA once a week from Chancellor Sheppard. It informs you that you have won 1,000 duelist points (DP). This may look like spam, but it is actually true. You only have one day to claim it, so keep checking your PDA and talk to the Dean to claim your points.
Duel Alongside Senjome
Talk to Senjome at the Blue Boys Dorm; he will invite to be his partner for a tag duel against Mokuma and Emperor Umiuma. If you win, Senjome will trust you, meaning he will be your partner for any duel.
Increase DP Anytime
Choose "Tag Duel" on Free Duel mode and set your DP to "2000." Pick any partner and choose two Novas as your opponents. You can earn up to 800 DP per duel, so keep playing these matches to make some easy points.
Midday Constellation Cheat
Enter the "Card Shop" and press the following combination of buttons: "Up," "Up," "Down," "Down," "Left," "Right," "Left," "Right," "X," "Circle." This will unlock the Midday Constellation Booster Pack.
Passwords
Enter these passwords into the "Password Machine" to unlock different cards: "27744077" will unlock the Absolute End card; "15150365" will unlock the White Magical Hat card; "80741828" unlocks the Witch's Apprentice card; "97687912" will unlock the Fairy Meteor Crush card; and "45311864" unlocks the Goblin Thief card.